Springville Branch (WBIC 1642200) and Viroqua WWTP Study WCR_08_09

Purpose

The purpose of this project is to collect water quality data to allow for the use of the Wisconsin DNR Small Stream Model (or equivalent) for determination of effluent limitations for the City of Viroqua WWTP. The city of Viroqua operates a 0.600 MGD wastewater treatment facility that discharges to the Springville Branch of the Bad Axe River. The wastewater effluent flows over karstic rock for approximately 2.75 miles above the Springville spring. Above the Springville spring the Springville Branch of the Bad Axe is a dry run channel classified as limited aquatic life in ch. NR 104. Below the spring, the Springville Branch of the Bad Axe River is managed as a Class I trout stream. Investigations by the department and the City have determined that the vast majority of the wastewater is lost to groundwater either through swallets or flow directly over exposed fractured bedrock prior to reaching the spring. Discharge of treated wastewater into fractured bedrock is an unacceptable practice and during the next permit cycle actions will need to be taken to remedy the situation. Alternatives include: 1. Treating effluent to groundwater standards. 2. Piping the effluent to surface water. 3. Constructing a catchment structure upstream of exposed bedrock and piping normal stream flow past the area of exposed bedrock to surface water. 4. Modify the streambed to reduce infiltration. This study will be continued for another year.

Objective

WW treatment alternatives include: 1. Treating effluent to groundwater standards. This would include a Total Nitrogen limit of 10 mg/l and a disinfection limit to yet to be defined but somewhere in the 0 total coliform to 0 fecal coliform range. 2. Piping the effluent to surface water. 3. Constructing a catchment structure upstream of exposed bedrock and piping normal stream flow past the area of exposed bedrock to surface water. This alternative would bypass the major sources of leakage during normal stream flows. During high stream flows, part of the flow would follow the existing stream bed and some infiltration would occur. 4. Modify the streambed to reduce infiltration. Except for option 1, these options would require a determination of surface water effluent limitations. Currently, the facility has BOD limitations of 20 mg/L monthly average and 30 mg/L weekly average. Using the “26 lb method” results in calculated effluent limitations of <10 mg/L weekly average for direct discharge to the trout stream reach, which the current treatment facility could not meet. We have concerns about using this method for small streams, given that it was developed for large rivers. In addition, the method is incapable of accounting for any in-stream BOD decay that may take place in the stream if option 3 or 4 were pursued. Incorrect calculations of water quality based limitations would either result in unnecessary capital and operation and maintenance costs by the City, or unacceptable impacts to this high quality fishery resource. The objective of this project is to collect data to allow for the use of the Wisconsin DNR Small Stream Model (or equivalent) for determination of effluent limitations for the City of Viroqua WWTP.

Outcome

Water chemistry will be collected (in 24 hr time composites) from the Springville Branch of the Bad Axe River above the spring (i.e. WWTP effluent) at three sites and analyzed for BOD5, CBOD5, ultimate CBOD, nitrogen series and chlorides during three sampling events. These data will be used to determine BOD/Ultimate CBOD ratios and decay coefficients for NBOD and CBOD. While it is expected that these decay rates may be different for a discharge to the Springville Branch of the Bad Axe River below the spring, they should provide a more reliable estimate of reaction rates than book values. Background water chemistry from the Springville Branch of the Bad Axe River below the spring will be collected for CBOD5, ultimate CBOD, nitrogen series and alkalinity during three sampling events. In addition, continuous dissolved oxygen, pH, temperature, and light intensity will be measured at three sites on a minimum of three occasions. Finally, time of travel, stream flow, and habitat data will be collected. These data will provide information on the background CBOD and nitrogen levels, dissolved oxygen and temperature and estimates of reaeration, photosynthesis, and respiration rates. Samples would be collected in July-Sept 2008. Data will be entered into SWIMS as results are received. Final report prepared by 3/31/09.

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Targeted Monitoring
Special Project
WCR_08_CMP09
2008
Complete
 
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